The present invention relates to a cell balance adjusting circuit, an abnormal cell voltage detecting circuit, a method of adjusting a cell balance and a method of detecting an abnormal cell voltage, and more particularly to a cell balance adjusting circuit for adjusting a balance between cells connected in series in an application circuit having combined secondary batteries with a simple control circuit configuration.
A conventional technique for charging combined secondary batteries such as lithium batteries will be described. FIG. 1 is a circuit diagram illustrative of a conventional circuit for charging combined secondary batteries such as lithium batteries. A series connection of first to sixth battery cells CE1, CE2, CE3, CE4, CES and CE6 is connected between a charging circuit 100 and a ground line. A voltage monitoring control circuit 200 is also provided. A first side of the first battery cell CE1 is connected to the charging circuit 100. The first side of the first battery cell CE1 is further connected through a first series connection of a first switch S1 and a first resistance R1 and also through a first by-pass to the voltage monitoring control circuit 200. A second side of the first battery cell CE1 is connected to a first side of the second battery cell CE2. The second side of the first battery cell CE1 and the first side of the second battery cell CE2 are further connected through a second series connection of a second switch S2 and a second resistance R2 and also through a second by-pass to the voltage monitoring control circuit 200. A second side of the second battery cell CE2 is connected to a first side of the third battery cell CE3. The second side of the second battery cell CE2 and the first side of the third battery cell CE3 are further connected through a third series connection of a third switch S3 and a third resistance R3 and also through a third by-pass to the voltage monitoring control circuit 200. A second side of the third battery cell CE3 is connected to a first side of the fourth battery cell CE4. The second side of the third battery cell CE3 and the first side of the fourth battery cell CE4 are further connected through a fourth series connection of a fourth switch S4 and a fourth resistance R4 and also through a fourth by-pass to the voltage monitoring control circuit 200. A second side of the fourth battery cell CE4 is connected to a first side of the fifth battery cell CE5. The second side of the fourth battery cell CE4 and the first side of the fifth battery cell CE5 are further connected through a fifth series connection of a fifth switch S5 and a fifth resistance R5 and also through a fifth by-pass to the voltage monitoring control circuit 200. A second side of the fifth battery cell CE5 is connected to a first side of the sixth battery cell CE6. The second side of the fifth battery cell CE5 and the first side of the sixth battery cell CE6 are further connected through a sixth series connection of a sixth switch S6 and a sixth resistance R6 and also through a sixth by-pass to the voltage monitoring control circuit 200. A second side of the sixth battery cell CE6 is connected to the ground line. The first series connection of the first switch S1 and the first resistance R1 is connected between the first and second side of the first battery cell CE1. The second series connection of the second switch S9 and the second resistance R2 is connected between the first and second side of the second battery cell CE2. The third series connection of the third switch S3 and the third resistance R3 is connected between the first and second side of the third battery cell CE3. The fourth series connection of the fourth switch S4 and the fourth resistance R4 is connected between the first and second side of the fourth battery cell CE4. The fifth series connection of the fifth switch S5 and the fifth resistance R5 is connected between the first and second side of the fifth battery cell CE5. The sixth series connection of the sixth switch S6 and the sixth resistance R6 is connected between the first and second side of the sixth battery cell CE6.
The voltage monitoring control circuit 200 monitors individual voltages of the first to sixth battery cells in the charge process. If one of the battery cells is completely charged up, then a charge current is by-passed to the corresponding resistance, whilst the remaining battery cells are continued to be charged.
In this case, the cell balance adjustment is made only in the charging process. If the capacitance balance of the cells is imperfect or lost, a dischargeable power in the discharge process is limited by a minimum cell capacity in the battery cells. This means that the large capacity cells show imperfect discharge. Namely, an unnecessary power is consumed in the charging process, and further the perfect discharge of the charged up power is difficult.
In order to have solved the above problem, the following conventional technique has been proposed, which is disclosed in Japanese laid-open patent publications Nos. 11-146570 and 11-098698. In the charging and discharging processes, a voltage across terminals of each cell is measured, so that two cells are selected on the basis of the measured voltage values. A charge accumulation device such as the capacitor is connected in parallel to first one of the selected two cells before this connected is switched into that the charge accumulation device is connected in parallel to second one of the selected two cells. This processes will be repeated to reduce the difference in voltage between the selected two cells.
Subsequently, the cell voltage is measured and then the above switching processes will further be repeated to take a balance among the individual cells. The use of the voltage judging circuit enables that the selected two cells have almost the same voltage. The voltage measuring operations will be repeated to adjust the voltage balances among the plural cells.
The conventional balance adjusting circuit using the charge accumulation device is thus capable of adjustment to the cell balance in the charge and discharge processes. The conventional balance adjusting circuit using the charge accumulation device, however, has the following problems.
The first problem is as follows. To select the two cells to be connected in parallel, it is necessary to measure the cell terminal voltages every times for judgement. The judgement and control circuit is made complicated. Particularly, in case of the large number of the battery cells connected in series, a large withstand voltage of the voltage measuring circuit is necessary.
A battery to be used for a hybrid car shows a high output voltage of 240V. In order to measure the cell voltage for judgement, the circuit is required to have an extremely high withstand voltage. This makes increased a cost or a price of the circuit.
To obtain a driving energy for the hybrid car, a high voltage is necessary. A responsible IC with a high withstand voltage for measuring and judgement to the voltage is expensive.
The second problem is as follows. Under the high voltage conditions, an averaged voltage difference between the comparing cells is about 1.2V if the cells are nickel hydrogen battery. The averaged voltage difference between the comparing cells is only 3.62V if the cells are lithium secondary battery. An accuracy in a few milli-voltage order is necessary to detect the voltage difference. Higher voltages in the range of 240V to 280V are used for the hybrid cars, electric cars and fuel battery cells. In such high voltage level, the accuracy in a few milli-voltage order is necessary for the circuit to detect the voltage difference. The circuit having such the high accuracy is expensive.
A large number of the small voltage cells is connected in series, for example, several tends to a few hundreds, so that a potential voltage from the ground level is 240V. This means that an extremely high d.c. voltage is applied to the circuit. By contrast, a voltage level for taking the balance between the cells is based on the low voltage level, for example, 1.2V or 3.6V. The accuracy in a few milli-voltage order is necessary for the circuit to detect the voltage difference. This means that the accuracy in ppm-order is necessary for the circuit to detect the voltage difference. Namely, the circuit is required to have the high withstand voltage and the high accuracy.
In the above circumstances, it had been required to develop a novel cell balance adjusting circuit, an abnormal cell voltage detecting circuit, a method of adjusting a cell balance and a method of detecting an abnormal cell voltage free from the above problem.
Accordingly, it is an object of the present invention to provide a novel cell balance adjusting circuit free from the above problems.
It is a further object of the present invention to provide a novel cell balance adjusting circuit with a simple circuit configuration and being capable of stably taking a highly accurate balance of a large number of series-connected battery cells having high output voltages.
It is a still further object of the present invention to provide a novel cell balance adjusting circuit which is not expensive.
It is yet a further object of the present invention to provide a novel cell voltage detecting circuit free from the above problems.
It is a further object of the present invention to provide a novel cell voltage detecting circuit with a simple circuit configuration and being capable of stably taking a highly accurate balance of a large number of series-connected battery cells having high output voltages.
It is a still further object of the present invention to provide a novel cell voltage detecting circuit which is not expensive.
It is yet a further object of the present invention to provide a novel method of adjusting a cell balance free from the above problems.
It is a further object of the present invention to provide a novel method of adjusting a cell balance with a simple circuit configuration and stably taking a highly accurate balance of a large number of series-connected battery cells having high output voltages.
It is a still further object of the present invention to provide a novel method of adjusting a cell balance at a low cost.
It is yet a further object of the present invention to provide a novel method of detecting a cell voltage free from the above problems.
It is a further object of the present invention to provide a novel method of detecting a cell voltage with a simple circuit configuration and stably taking a highly accurate balance of a large number of series-connected battery cells having high output voltages.
It is a still further object of the present invention to provide a novel method of detecting a cell voltage at a low cost.
In accordance with the present invention, a cell balance adjusting circuit comprises: a series connection of basic cells; and a voltage holder connected through a switching circuit to individual terminals of the basic cells, wherein the switching circuit shows a switching operation to provide a parallel connection between an intermediate point between adjacent two of the basic cells and the voltage holder, and the switching circuit shows a unidirectional sequential scanning of the switching operation to all of the basic cells, and the switching circuit repeats the unidirectional sequential scanning.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.